Production Scheduling and Customer Orders Assignment in a Three-Level Supply Chain

In the classical production-distribution centers problem, only assignment of customers, distribution centers, and suppliers is determined. This paper extends the problem of production-distribution centers assignment by considering sequencing decisions in the supply network. Nowadays, meeting delivery time of products is a competitive benefit; therefore, the objective is to minimize total tardiness. This problem is mathematically formulated by a mixed integer programming model. Then, using the proposed model, small instances of the problem can be optimally solved by GAMS software. Moreover, two metaheuristics based on variable neighborhood search and simulated annealing are proposed to solve large instances of the problem. Finally, performance of the proposed metaheuristics is evaluated by two sets of balanced and unbalanced instances. The computational results show the superiority of the variable neighborhood search algorithm. 1. Introduction In the supply chain, various organizations work together for converting raw materials to finished products and are connected with each other over far distances. The customer orders due date and the short life-cycle products need agile supply networks. To accelerate supply chain operations many activities such as keeping storage which are nonvalue added activities must be eliminated. It also should be stated that customer demands are generating the flow of supply network and they have to be specified or predicted in advance, but optimization of this flow through the network for minimizing the costs is an important purpose of the supply chain and, for optimizing, speed of the sources and capacity limitations are considered. Scheduling for order shipment to the customer destinations and using transportation means, in order to pick up the orders at the distribution centers (DCs) were done just by staff experiences. This will increase not only the waiting time of transportation means, but also accumulation of the orders and inventory costs. Ultimately delivery time of the orders will exceed the due date and cause penalty costs and dissatisfaction of the customers. The model which is proposed in this paper presents a good solution for the above situation. It offers a good method for calculating the time of production or packing in the plants and distribution centers and the transportation between them to decrease the delivery time of the orders and define an optimal assignment and sequence for the customers according to the capacity of distribution centers and customer due dates. As regards the importance of scheduling